1. Field of the Invention
The present invention relates to a manufacturing method of bumps and a manufacturing method of a pixel structure having the bumps. More particularly, the present invention relates to a manufacturing method of asymmetric bumps capable of reducing the number of required photomasks and a manufacturing method of a pixel structure having the asymmetric bumps.
2. Description of Related Art
Thin film transistor liquid crystal displays (TFT-LCDs) can be categorized into transmissive TFT-LCDs, reflective TFT-LCDs, and transflective TFT-LCDs based on the way to utilize light sources. In a transmissive pixel structure, a transparent conductive material is used to form a transparent pixel electrode of the transmissive pixel structure, and required light is supplied by a backlight source. After passing through the transparent pixel electrode, the light can serve as a light source required by image display.
In a reflective pixel structure, a conductive material capable of reflecting light is frequently used to form a pixel electrode of the pixel structure. Thereby, an external light incident to the pixel electrode can be reflected for providing a light source required by image display. In a transflective pixel structure, each pixel electrode is formed by a reflective conductive thin film and a transparent conductive thin film, and the backlight source and an external light source are employed simultaneously. In said reflective pixel structure and said transflective pixel structure, a plurality of bumps is often formed for improving light reflectivity.
FIGS. 1A to 1B are schematic flowcharts illustrating partial fabrication of a conventional pixel structure having symmetric bumps. Referring to FIG. 1A, first, a film layer 120 is formed on a substrate 110 having a light transmitting region 112 and a light reflecting region 114. Next, a patterning process is performed on the film layer 120 with use of a photomask 100a. Here, the photomask 100a has an opaque region 102 and a transparent region 104. Specifically, the film layer 120 is irradiated by an exposure light beam L, and a development process is performed on the exposed film layer 120. After that, the film layer 120 in the light transmitting region 112 is removed. Referring to FIG. 1B, a gray-scale photomask 100b having a plurality of opaque regions 102 and a plurality of transparent regions 104 is provided. Another patterning process is performed on the film layer 120 in the light reflecting region 114 through the opaque regions 102 of the gray-scale photomask 100b, so as to form a plurality of symmetric bumps 126.
Based on the above, two photomasks are required for removing the film layer 120 in the light transmitting region 112 and forming the symmetric bumps 126 in the light reflecting region 114. As a result, the manufacturing process of the conventional pixel structure having the symmetric bumps 126 is rather complicated and time-consuming.
FIG. 2 is a schematic flowchart illustrating partial fabrication of another conventional pixel structure having symmetric bumps. Referring to FIG. 2, a half-tone photomask 100c, having a plurality of opaque regions 102, a transparent region 104 and a plurality of semi-transparent regions 106, is provided. A patterning process is performed on the film layer 120 with use of the half-tone photomask 100c. As such, only one photomask is required for fabricating the light transmitting region 112 and the symmetric bumps 126 in the light reflecting region 114 at the same time.
However, the manufacturing methods depicted in FIG. 1A, FIG. 1B and FIG. 2 are merely applicable to fabrication of the symmetric bumps 126 which are not capable of reflecting external light in an effective manner. To improve reflection of external light, a method of manufacturing a pixel structure having asymmetric bumps was proposed as indicated below.
FIGS. 3A to 3B are schematic flowcharts illustrating partial fabrication of a conventional pixel structure having asymmetric bumps. Referring to FIGS. 1A to 1B and FIGS. 3A to 3B, after the symmetric bumps 126 are formed by performing the steps shown in FIGS. 1A to 1B, another patterning process is performed on the symmetric bumps 126 (depicted in FIG. 1B) with use of another photomask 100d as shown in FIG. 3A. In the photomask 100d, the opaque regions 102 are randomly distributed. After the implementation of said patterning process, the symmetric bumps 126 become asymmetric bumps 128 as shown in FIG. 3B. Nonetheless, the method of manufacturing the asymmetric bumps 128 still requires at least two photomasks, which is rather uneconomical.
FIGS. 4A to 4B are schematic flowcharts illustrating partial fabrication of another conventional pixel structure having asymmetric bumps. Referring to FIG. 4A, a patterning process is performed on the film layer 120 with use of a gray-scale photomask 100e in which the opaque regions 102 are irregularly arranged. Thereby, light interference results in uneven exposure of the film layer 120.
As indicated in FIG. 4B, after a development process is performed on the exposed film layer 120, asymmetric bumps 128′ with different heights are formed. Although only one gray-scale photomask 100e is required for manufacturing the asymmetric bumps 128′, height difference of the asymmetric bumps 128′ is quite significant, thus posing a negative impact on light reflectivity of the asymmetric bumps 128′.
As such, how to form uniform asymmetric bumps characterized by great light reflectivity with use of few photomasks has become an imperative research issue.